1. Field of the Invention
This invention relates to a thin film magnetic structure for use in a magnetic head of a disc storage apparatus, and more particularly, for use in a magnetic head having a magnetic circuit and a coil are formed of thin films, and the method of fabricating the thin film magnetic structure.
2. Description of the Prior Art
It has been recognized that distinguished advances have occured in the technology of magnetic disc storage apparatus with significant improvement in storage capacity, and a single disc with 3.5 inches diameter can store several hundred mega bytes of data on it. For further improvement in storage capacity in high-density recording environments, it is required to make the width of a track on a disc even smaller and to record data with higher density in each track. In order to satisfy this requirement, interests in thin film magnetic heads having a fine structure to be used as a read-and-write head have been increased. This kind of magnetic head is made by integrating all the functional components such as magnetic cores and coils in the form of thin films on a single substrate by means of semiconductor fabricating technologies. In the following, a structural example of a general thin film magnetic head is explained referring to FIGS. 1 and 2.
A coil 30 shown at the center of FIG. 1 is a spiral coil, and a magnetic core 10 is composed of a pair of magnetic pole films 15 and 16 shaped like the cross-section of an onion between which a part of the coil 30 is placed. In the top part 10a of the magnetic core 10, a read-and-write gap G having a narrow gap width w is formed between magnetic pole films 15 and 16, and a magnetic circuit is defined by contacting the other end parts of magnetic pole films 15 and 16 to each other at the base part 10b of the magnetic core 10. Where the gap G is placed close to or in contact with a surface of a disc, the magnetic head formed as in the above structure can write data on the disc by leading electric current into the coil 30 through a pair of lead lines 30a and 30b and the magnetic head can read data on the disc by detecting induced electric current in the coil 30.
FIG. 2 is a cross-sectional view through line X--X of FIG. 1, showing an enlarged cross-sectional view of the read-and-write gap. A lower-side magnetic pole film 15 composed of magnetic materials such as Permalloy having a thickness between 1 .mu.m and 2 .mu.m is placed on a substrate 1 made of alumina, and a gap film 20 composed of alumina or silicon oxide having a thickness less than 0.5 .mu.m is provided above the lower-side magnetic pole film 15. In the example shown in FIGS. 1 and 2, the coil 30 has two-layered turns, a lower-side coil 31 and an upper-side coil 32, both of which are formed by photo-etching processing of thin films deposited by vacuum evaporation or sputtering of copper or aluminum in the form of spiral patterns and are covered with a lower insulating film 33 and an upper insulating film 34 made of silicon oxide or polyimide. The coil 30 is inserted between the lower magnetic pole film 15 and the upper magnetic pole film 16 and the magnetic core 10 is formed in such a manner that the both the upper side magnetic pole film 16 and the lower-side magnetic pole film 15 contact the gap film 20 at the top part 10a. The read-and-write gap G is formed by lapping processing of the outer face of the top part 10a and the read-and-write gap G has a narrow gap length g defined by the thickness of the gap film 20 between the magnetic pole films 15 and 16. This kind of thin film magnetic head shown in FIGS. 1 and 2 is disclosed in, for example, laid-open Japanese Patent Application No. 84019/1980.
In the above described kind of thin film magnetic head, current semiconductor processing technologies for precisely defining the gap width w and the gap length g, present the reduction of the track width on a disc and a high recording density on the track to a certain degree. However, the performance of the magnetic head in recording and reading data on a disc is strongly influenced by the magnetic characteristics of magnetic materials used for the magnetic core 10. Specifically, as the signal frequency in reading data on a disc goes up to several MHz, it is required to use magnetic materials having a high magnetic permeability in a high frequency region for forming the magnetic head. In order to satisfy this requirement, anisotropic magnetic materials are often used and the axis of easy magnetization is fixed in the direction that the head gap width w is defined. This structure is explained in FIG. 3.
FIG. 3 is an enlarged view of the top part 10a of the lower magnetic pole film 15 of the magnetic core 10 where static magnetic domains without application of outer magnetic fields are shown. Magnetic domain walls are categorized into a Bloch magnetic domain wall, or 180-degree magnetic domain wall B18, which is a boundary of two adjacent magnetic domains having their magnetization directions opposite to each other, and a Neel magnetic domain wall, or 90-degree magnetic domain wall B9, which is a boundary of the adjacent magnetic domains having their magnetization directions vertical to each other. Therefore, in the magnetic pole film, as shown in FIG. 3, magnetic domains are composed of either hexagonal magnetic domains H or triangle magnetic domains T, and unless the head width w is large, magnetic domain configuration is such that hexagonal magnetic domains H expand and occupy the center of the head and triangle magnetic domains T are placed aside hexagonal magnetic domains H. Arrows in hexagonal magnetic domain H show directions of axes of easy magnetization which are parallel to the direction in which the head width w is defined. In reading and writing data on a disc, as magnetization force is applied in the direction vertical to the direction in which the head width w is defined, magnetic walls of hexagonal magnetic domains H are displaced in response to the magnetization force to rotate the magnetization directions of domains H 90 degrees. This manner of rotating magnetization direction of hexagonal magnetic domains H requires less energy as opposed to reversing the magnetization direction in the opposite direction. Such rotation of magnetization direction permits a higher magnetic permeability to be obtained.
However, if the gap width w is reduced to less than about 10 .mu.m and the gap length g is reduced to less than about 0.5 .mu.m, it is difficult to obtain a higher magnetic permeability. One reason is that where the gap width w is made small the area occupied by triangle magnetic domains T becomes greater than that occupied by hexagonal magnetic domains H. The other reason is that an the eddy current loss increases in the magnetic core 10 as the gap length g is made smaller for increasing the signal frequency for reading and writing data. A well-known solution to this problem is to form the magnetic core 10 in the form of multiple layered films. In IBM Disclosure Bulletin, Vol, 21, No. 11, 1939, pp. 4361, there is disclosed a structure in which a film made of Permalloy and a film made of silicon oxide are alternately laminated for forming multiplied layered films. In this structure, the eddy current loss is reduced by means of forming a thin film of Permalloy. Further, by making the thickness of films of silicon oxide small enough, thin films of Permalloy sandwiching a film of silicon oxide can be sufficiently coupled magnetically to form a magnetic circuit so that the growth of triangle magnetic domains T may be limited and hexagonal magnetic domains H may be enlarged dominantly. Furthermore, Japanese Patent Laying-open Nos. 4908/1989 and 42011/1989, disclose technologies in which Permalloy series alloys are used in order to solve the above mentioned problems in a similar way. In addition, in laid-open Japanese Patent Application No. 51515/1985, a magnetic head having multiple layered films made of Fe-Si alloys is disclosed.
However, as a practical manner, improvement in the magnetic permeability of multiple layered magnetic materials, is not easily attained. In particular, when, magnetic materials having a high coercive force are used for the magnetic recording media to improve signal level for high-density recording environments. For writing data on a magnetic disc made of this type of magnetic recording media, requires magnetic materials having high saturation magnetic flux density to form the magnetic core of the magnetic head. Under these conditions, it is very difficult to attain high magnetic permeability with multiple layered magnetic materials.
For example, the coercive force of the magnetic recording media used in the MIG (Metal In Gap) method may be employed up to 1500 Oe. A magnetic head using magnetic materials such as Permalloy can not give this kind of magnetic recording media enough energy. Therefore, it is required to use amorphous magnetic materials such as Mo-Permalloy alloys. From experimental observations, it has been proven that the magnetic permeability of multiple layered thin films formed with amorphous magnetic materials and silicon oxide is half the expected value of the magnetic permeability. Even by changing experimental conditions such as sputtering parameters and film thickness of magnetic films and silicon oxide films, no no prospective, practical use of the above mentioned materials and structure of multiple layered thin films have been found. In the above experiments, frequency dependence of magnetic permeability of multiple layered thin films was found to be rather good as a result of a multiple layered structure. This has been interpreted to mean that the generic property of high permeability magnetic materials is not reflected in individual magnetic thin films formed as above, and hence higher magnetic permeability can not be obtained.